The invention involves a digital printer or copier machine with an overheating protection device.
For certain commercial printer or copier machines, a latent electrostatic image is developed by charged toner particles. These particles are transferred onto an image receiving substrate, hereinafter referred to simply as xe2x80x9csubstratexe2x80x9d. Afterwards, the developed image that has been transferred onto the substrate is fixed by the toner particles being fused by supplying them with heat. This operation occurs in a fixing device.
Fixing devices are known in which hot cylinders or rollers are used to fix the toner onto the substrate or in order to preheat the substrate that may already have the toner image. The heating of the hot, customarily hollow cylindrical fixing rollers is done from the inside via their inner sheath surface and/or from the outside using at least one heated auxiliary roller that is in rolling contact with the fixing roller, or at least one radiation device that impinges the fixing roller with electromagnetic radiation. Furthermore, fixing devices are known in which the fixing of the toner image and possibly, the preheating of the substrate, is started directly by a radiation device without an intermediate connection of fixing rollers, and by using them, the toner can be fused in a non-contact manner.
The known radiation devices have at least one lamp that, for example, radiates ultraviolet light and visible or infrared light. The known lamps customarily have a quartz glass bulb that can heat up to 800xc2x0 C. when the radiation device is turned on. Furthermore, ceramic radiators are known that have temperatures up to 1200xc2x0 C. on their outer side. Disadvantageous in the previously described radiation devices based on their very high temperatures is that there is a danger of fire. This danger occurs especially during a paper jam, when the substrate that consists of paper, for example, is arranged opposite the radiation device (then turned off) and exposed to its heat radiation. The paper can start to arch as a result so that it comes into contact with the lamp, or parts heated up by it, and can ignite in the process. Furthermore, there is the possibility that the paper has a deformation, such as a dog-ear, whereby contact can also occur between the paper and the radiation device.
In order to prevent contact between the paper and the radiation device, devices are used to protect the substrate from excessive heating. From the U.S. Pat. No. 5,068,684, a protection device is provided with flaps arranged in a radiation path of a radiation source. These flaps can be moved into an open and closed position. As soon as the radiation source is turned off, the flaps are closed in order to shield the paper arranged in the radiation path from the heat radiation.
A protection device with rotationally movable sealing flaps and/or screens is provided in U.S. Pat. No. 6,085,060.
From the patent DE 2298 18 588 U1, a fixing device for an electrophotographic printer or copier device is known, in which to protect the paper to be printed from excessive heating, a radiation device is used which is constructed in two parts. The two parts are constructed so that they can be positioned crosswise to the paper transport device. The fixing device is controlled in such a way that during a paper stop, the two parts of the radiation device are driven far enough apart from each other in opposite directions, so that the paper no longer is impinged by their heat radiation.
Based on the constructive embodiment, in particular because of their movable screens, flaps, and/or parts of the radiation devices, the previously described protection devices have an expensive and thus cost intensive design. Furthermore, they are susceptible to damage and require an increased maintenance expense.
From U.S. Pat. No. 4,019,054, a fixing device that has a radiation device is known in which a fixed metal plate arranged opposite the radiation device is located in the radiation path. The metal plate, which is completely solid, has a prearranged intake area, as seen in the transport direction of the substrate that is passed by it. In the intake area, the substrate should be preheated. An outlet area follows this, in which many throughput openings that have a large open cross section are made in the metal plate, so that the electromagnetic radiation penetrates the metal plate in an almost unhindered manner and the substrate with the toner image can heat up. It is a disadvantage in this device that the metal plate is heated so much by the radiation device that the paper can ignite upon contact with it.
The purpose of the invention is to provide a printer or copier machine and a protection device, in which a contact between the substrate and the radiation device can be practically ruled out. Furthermore, the protection device should have a simple and thus cost effective design.
In order to achieve this purpose, a printer or copier machine is proposed which has a fixing device for fixing a toner image onto a substrate, for example a paper sheet or a paper web, and is guided along a transport path. The fixing device contains at least one radiation device, by the use of which at least one side of the substrate can be impinged with electromagnetic radiation. Finally, a device for protection against excessive heating of the substrate, especially during an interruption of the substrate transport, is provided. The printer or copier machine is characterized in that the protection device has at least one stopper arranged fixed in the radiation path between the radiation device and the transport path of the substrate, which prevents a contact between the substrate and the radiation device. The stopper is thus constructed in such a manner according to the invention that, for example, when the substrate arches up in the direction of the radiation device or if there is a bend in the substrate, it stops on the stopper. In this way, it can be ensured that the substrate cannot ignite on the turned off radiation device or by parts of the machine heated by it during its normal operation.
In relation to the invention presented, the term xe2x80x9cfixedxe2x80x9d is understood to mean that the stopper is installed in a housing or the like in such a way that its position does not change within the printer or copier machine. This means the stopper can not be moved relative to the substrate transport plane and the radiation device, but instead is arranged fixed in location and thus in the installed condition is always located in the radiation path, both during the fixing of the toner image on the substrate and during an interruption of the substrate transport. The protection device, differing from the known protection devices, has no movable parts in the sense of, for example, parts that can rotate or tilt, and thus represents a passively acting solution for the protection of the substrate against excessive heating and ignition as a result of a contact between the substrate and the radiation device and/or parts heated by it. Because of its simple construction, the protection device according to the invention can be manufactured in a cost effective manner. Moreover, a compact and space saving construction is possible.
It is noted that an ignition of the substrate can only be ruled out with certainty if the radiation device is turned off quickly and safely during a substrate stop and if necessary, when the speed of the substrate has fallen below a certain, preferably adjustable, substrate transport speed. This is usually done automatically. As of that moment, the stopper and the substrate arranged in the radiation path are then only still impinged with the heat radiated off of the hot parts of the radiation device or other structural parts of the machine heated in the operation of the radiation device.
The stopper arranged in the radiation path is constructed in such a way in a preferred embodiment form that it does not prevent the fusing of the toner image. For this purpose, it is arranged at a distance from the substrate transport plane so that in the normal print and/or copier operation of the machine, the substrates are guided by it without coming into contact with the stopper in the process. The stopper is then only effective if a substrate stop occurs within the fixing device and the substrate becomes arched and/or arches in the direction of the radiation device as a result of excessive heating. Preferably, the radiation absorption of the stopper is only low when a radiation device is turned on.
In a preferred embodiment form, the stopper is formed from at least one mesh structure that lets the electromagnetic radiation radiated out by the radiation device in the direction of the substrate to pass through it in an approximate unhindered manner. The mesh structure has a sieve or net type structure, whereby the width of its mesh is relatively large. In each case, the meshes are at least so small, however, that a substrate with a bent corner (dog-ear), also stops on the mesh structure when the substrate arches up in the direction of the radiation device, for example, so that a contact between the substrate and the radiation device, especially between the quartz glass of the lamp, possibly, a reflector surrounding the lamp, or otherwise by the parts of the machine heated when the radiation device is turned on, is prevented with a large degree of certainty.
The mesh structure preferably having only a small thickness is constructed so that it is planar, i.e., it has two flat sides like a plate and is arranged in the radiation path either parallel to the substrate transport plane or inclined towards it. The arrangement of the mesh structure in any case is such that the flat side of the mesh structure facing towards the substrate transport plane forms the stopper surface for the substrate. Of course, several layers of the mesh structure could also be used.
According to a further embodiment of the invention, the material of the mesh structure has only a low heating capacity and/or only a low heat conductivity. The low heating capacity and heating conductivity of the mesh structure is an advantage to the extent that the substrate, upon contact with the mesh structure, does not ignite by the heat stored by the mesh structure.
Especially preferred is an embodiment example of the machine, which is characterized in that the mesh structure is formed from at least one mesh braid. The mesh braid is made out of individual threads that are woven, linked, or in any other way preferably detachably connected together. In another embodiment variation it is provided that the xe2x80x9cthreadsxe2x80x9d are connected to each other so that they are at least partially undetachable; for example, the threads can be fused together, adhered, soldered, or in another way firmly connected. In this case, the mesh braid has a grid structure. Preferably, the mesh braid is very wide meshed, i.e., it has a large mesh width, which for example, can be 10 mm and less. In each case, the meshes are only so large, however, that as mentioned contact between the radiation device that has been turned off in the event of a malfunction and the substrate that arches up in the direction of the radiation device can be ruled out with certainty.
The threads can be made out of a wide range of materials that have the properties described above with regard to the heat conductivity and heat capacity. The threads can, for example, be made out of a suitable metal, heat resistant plastic, glass and/or carbon fibers. Gold coated tungsten wires that have a diameter of approximately 100 xcexcm or smaller have proven to be especially preferred. It is also readily possible to use wires with a diameter of larger than 100 xcexcm. Provided the mesh structure is not a mesh braid, but instead for example, is a plate or sheet that is provided with openings having a very small diameter, metal can also be used for this purpose, in particular tungsten, heat resistant plastic, or the like.
Furthermore, an embodiment example of the invention is preferred in which the at least one stopper is formed from a thin, preferably sheet like plate, which is arranged fixed in the radiation path and at a distance from the transport plane of the substrate.
According to a first embodiment variation, the plate xe2x80x9cstandsxe2x80x9d almost on edge on the substrate transport plane, i.e., its flat sides run perpendicularly to the transport plane. Because of this arrangement, the surface covered by the plate in the radiation path is extremely small and the large portion of the electromagnetic radiation radiated from the radiation device radiates past the plate onto the substrate transport plane. Because of this arrangement, the boundary edge of the plate facing towards the substrate transport plane forms the surface that stops the substrate and that is only very small. The plate is oriented in a preferred embodiment form in the transport direction of the substrate, i.e., the flat sides of the plate run at least essentially parallel to the substrate transport direction. Of course, it is also possible that the at least one plate running perpendicularly to the transport plane, runs at an angle or crosswise to the transport direction. It is important that if the substrate leaves its transport plane, whether by a deformation, for example, arching as a result of excessive heating, or any other deformation, for example, a bent edge, it stops on the at least one plate and does not come into contact with the radiation device.
According to a second embodiment variation, the plate is inclined by a certain angle, as seen relative to the substrate transport plane in and/or crosswise to the transport direction of the substrate, so that the electromagnetic radiation radiated out from the radiation device has a minimal interaction area with the plate.
In all embodiment forms of the plate that functions as the stopper, it is common that they consist of a temperature resistant material, and that they are preferably not deformed or damaged when the radiation device is turned on. Provided the electromagnetic radiation has a UV portion, preferably a material is used that is resistant against ultraviolet radiation.
The object of the invention also involves a device for protecting an object that is guided past a radiation device against excessive heating, whereby the protection device has at least one stopper arranged fixed in the radiation path between the radiation device and the object to be heated. The protection device can be used for a digital printer or copier machine. The object to be protected is, for example, a substrate that should be preheated using the radiation device or that has an unfixed toner image that is fused using the radiation device.
Therefore, to achieve the purpose of the invention, a digital printer or copier machine is proposed characterized in that the protection device has at least two protection elements that are permeable to electromagnetic radiation and arranged in the radiation path between the radiation device and the transport path of the substrate and at a distance from each other. The radiation device is located on one side of the first protection element, while the substrate transport plane is located on an opposite side of the second protection element. The intermediate space between the protection elements is preferably free of installed parts. The protection elements are preferably constructed in such a way that when the radiation device is turned on, the radiation output arriving onto the toner image that is transferred onto the substrate still is up to 95% of the radiation output given off by the radiation device, whereas when the radiation device is turned off, the remaining heat radiation is almost completely absorbed by the protection elements and, in the end, only a small heat quantity, for example, only approximately 10% of the initial energy of the residual heat radiation of the radiation device, arrives at the substrate. Because of these properties, the heating of the second protection element that functions, among other things, as a stopper for the substrate, is only relatively low so that upon contact between the second protection element and the substrate, the substrate can not ignite on the second protection element. If necessary, for this purpose, the second protection element can be cooled for this purpose, for example, using air. The largest part of the energy of the residual heat radiation when the radiation device is turned off is thus received by the first protection element, whose temperature can thus be noticeably above the temperature of the first protection element. The protection elements act almost as a filter for the electromagnetic radiation in a wavelength range which corresponds to that of the residual heat radiation of the radiation device that is turned off.
In an especially preferred embodiment form, the protection elements are each formed from at least one plate, and each plate consists of a material such as quartz glass that is permeable to electromagnetic radiation. The plates can each be completely solid, i.e., their flat sides have no openings or other passages through them. When the radiation device is turned on, its emitted electromagnetic radiation must thus penetrate through the at least two plates in order to get onto the toner image. The plates are preferably arranged parallel to each other and to the substrate transport plane.
In an especially preferred advantageous embodiment example, it is provided that the protection elements that are plate shaped or each formed from at least one light permeable plate consist of a material that lets through electromagnetic radiation at a wavelength xcex from approximately 0.2 xcexcm to approximately 6 xcexcm, preferably from 0.2 xcexcm to 3.5 xcexcm, and in particular from 0.2 xcexcm to 2.5 xcexcm. The protection elements thus function as a filter for the electromagnetic radiation, so that only a certain radiation spectrum is permitted through to the substrate.
According to the invention it is planned that the radiation device, when it is turned on, preferably radiates ultraviolet light, visible light or near infrared light, whereby the largest part of the radiation energy is allowed through to the substrate by the protection elements/plates according to the invention. When the radiation device is turned off, the protection elements are still impinged by the heat radiation (in particular, infrared to far infrared) of the structural parts heated by the radiation device, for example, the quartz glass structure of the radiation source. This radiation is as mentioned however, for the most part absorbed by the protection elements, in particular, by the first protection element arranged opposite the radiation device.
The protection elements can be manufactured out of the same material or out of different materials. As a material for the protection elements, quartz glass can be used, for example.
In an advantageous embodiment example, the intermediate space between the protection elements can be flushed by a gaseous medium, especially air, functioning to cool the protection elements. The air functions both for the cooling of the first as well as the second protection element.
According to an additional embodiment of the invention it is provided that the protection elements are arranged fixed relative to the transport plane of the substrate and/or the radiation device. The protection elements thus have a fixed, constant position within the radiation path, and thus must not, when there is a malfunction of the printer/copier operation, be moved first into the radiation path and then back again into a maintenance position, and this simplifies the construction of the protection device.
Finally, the object of the invention also involves a device, especially for a digital printer or copier machine, for protecting an object guided past a radiation device from excessive heating, which is characterized in that it has at least two protection elements that are permeable to radiation and arranged at a distance from each other, which are arranged in the radiation path between the radiation device and the object to be heated. The object can, for example, be the substrate itself, which is moved as a result of a malfunction out of its transport plane, for example, in which it becomes arched, and stops on the protection element arranged opposite it. It is also conceivable that the object is a cylinder or roller heated on the outside using the radiation device, on the outer sheath surface of which, if necessary, the substrate adheres in an undesired manner and in this way gets out of its transport plane into a position opposite the radiation device. Furthermore, the object can be a conveyor belt that functions for the transport of the substrate. In all cases, the protection elements prevent a direct contact between the object mentioned and the radiation device, whereby the protection element lying opposite the object arranged in the radiation path possibly functions as a stopper. According to the invention, it is provided that the protection element functioning as a stopper is only heated until upon contact between the object, in particular, the substrate, and this protection element, an ignition of the substrate can be ruled out with certainty.